I. Field of the Invention
The present invention relates generally to toolholder assemblies and, more particularly, to a quick release toolholder assembly.
II. Description of the Prior Art
There are many previously known toolholders of the type used in manufacturing operations. These toolholders typically comprise a chuck having a collet for securing a tool, such as a drill, reamer or the like, coaxially to the chuck. The chuck, in turn, includes an elongated shank which is inserted into a receiving bore on a rotatably driven spindle. The spindle bore is coaxial with the axis of rotation of the spindle so that, in the ideal situation, the tool secured by the collet to the chuck is coaxial with the axis of rotation of the spindle.
In one type of previously known toolholder assembly, cooperating conical surfaces are formed on both the chuck shank as well as the spindle bore in order to center the axis of the chuck with the axis of the spindle. In other cases, however, both the spindle bore as well as the chuck shank are cylindrical in shape and are simply machined to sufficiently close tolerances to ensure that the axis of the chuck is coaxial with the axis of the spindle.
Following insertion of the chuck shank into the spindle bore, there are at least two different commonly used means for releasably securing the chuck to the spindle. In the first, an internally threaded collar is rotatably mounted on the chuck. This internally threaded collar rotatably engages external threads formed on either the spindle or an adapter mounted to the spindle. Consequently, as the threaded collar is tightened onto the spindle, the chuck is moved into its operative position with respect to the spindle. In the case of cooperating conical surfaces, the conical surfaces mate against each other to center the chuck with respect to the spindle. In the case of a cylindrical shank, rotation of the collar causes a flat machine at the end of the spindle to flatly abut against a flat machine on the chuck in order to secure the chuck to the spindle against movement.
In still a further type of toolholder assembly, a ball lock arrangement is provided for releasably securing the chuck to the spindle. In the conventional ball lock arrangement, a plurality of balls are carried by the spindle which face a receiving groove formed in the chuck once the chuck is inserted into the spindle bore to its operative position. An axially slidable sleeve is mounted to the spindle and movable between a locked and unlocked position. In its locked position, the sleeve includes a cam surface which presses the balls into the receiving groove on the chuck thus locking the chuck to the spindle against axial movement. Conversely, in its unlocked position, the sleeve cam surface is retracted away from the balls thus allowing the balls to move radially outwardly and enable both the insertion and removal of the chuck from the spindle bore.
A primary advantage of the previously known toolholder assemblies having a ball lock for securing the chuck to the spindle is that chucks having different tools may be rapidly changed for the spindle.
A primary disadvantage, however, of the previously known toolholder assemblies utilizing a ball lock is that the ball lock provides a less secure attachment between the chuck and the spindle than obtainable by the previously known threaded collar locking arrangements. Consequently, these previously known toolholder assemblies utilizing a ball lock have been known to rock slightly during machining operations. For that reason, such ball lock assemblies are oftentimes called xe2x80x9crockersxe2x80x9d in the industry.
The present invention provides a ball lock toolholder assembly which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the toolholder assembly of the present invention comprises an elongated spindle adapted to be rotatably driven about a longitudinal axis. The spindle also includes a longitudinally extending bore open at one end. The bore is generally cylindrical in shape and preferably has a conical section adjacent the open end of the bore.
A chuck includes a conventional collet for securing a tool, such as a drill, coaxially to the chuck. The chuck also includes an elongated shank which is adapted for insertion into the spindle bore as well as a conical section which is complementary to the conical section formed adjacent the open end of the spindle bore. These conical surfaces cooperate to center the axis of the chuck with the axis of the spindle.
A plurality of circumferentially spaced and radially movable balls are carried by an annulus mounted to the spindle adjacent its open end. These balls register with an annular groove formed around the outer periphery of the chuck when the chuck is inserted into the spindle to its operative position.
In order to lock the chuck to the spindle in its operative position, an annular sleeve is coaxially mounted to the spindle at the open end of the bore. The sleeve is axially movable between a locked and an unlocked position. In its locked position, a cam surface formed on the interior of the sleeve cooperates with the balls to force the balls radially inwardly into the chuck recess thus locking the chuck to the spindle. Conversely, in its unlocked position, the sleeve cam surface is retracted away from the balls to permit the balls to move radially outwardly thereby releasing the chuck from the spindle.
In order to prevent rocking of the chuck relative to the spindle, a piston having a conical surface coaxial with the axis of the spindle is mounted to the spindle at the innermost end of the spindle bore. This piston is axially movable between a first and second position in which the first position is closer to the open end of the spindle bore than the second position. A helical compression spring urges the piston towards its first position while a fastener extending through the piston limits the axial movement of the piston as well as maintains the piston coaxial with the axis of the spindle.
A conical surface is also formed on the outer periphery of the chuck shank at its free end. Thus, upon insertion of the chuck shank into the spindle bore to the operative position of the chuck, the conical surfaces on the piston and shank end engage each other so that the piston both supports the free end of the chuck shank and also maintains the free end of the chuck shank coaxial with the axis of rotation of the spindle. Consequently, since the chuck is supported by the spindle at both its forward and rearward end, any xe2x80x9crockingxe2x80x9d of the chuck relative to the spindle is effectively precluded.
A lubricant passageway is also optionally provided through the piston fastener and registering lubricant passageway formed in the chuck shank.